Fancy catching up with some of the sights around the Czech Republic, how does Toxic Mountain sound as a field trip? Hmmm, perhaps not so alluring. Toxic Mountain is the translation of Jedovar Har, to the south of Prague, where for 130 years iron and mercury have been mined and smelted. Maria Hojdova from here in Prague, has been analysing mercury levels from the forest floors around Jedovar Har, and another site, Pribram, where lead zinc and silver were mined and lead smelted, leaving mercury behind from the ores.
Hojdova found that most of the inorganic mercury was present as the immobile and water insoluble mercury sulfide, with less than 14% of the mercury in more mobile forms – this was also backed up by showing that most contamination was on the surface of soil, rather than permeating further down. By also analysing the mercury in tree rings Hojdova also showed how the mercury deposition matched the activity of the mining areas, including a secondary peak in the 60s.
However, if that doesn’t put you off, Hojdova did conclude her talk with a recommendation for Pribram and its mining museum. Unfortunately, I don’t think my schedules going to allow such a field trip.
Meanwhile, over in the poster sessions I was treated to a fantastic story of art theft and recovery by a student from Karel Lemr‘s lab, Volodymyr Pauk. The lab were approached when n painting, Crucifixion, stolen from the St Sebestian church on Holy Hill in the Czech Republic, was recovered in Austria. Restorers and conservators obviously wanted to know what they had, both to determine authenticity and to help restoration efforts. Pauk was charged with determining which blue pigment was used – Prussian blue or indigo.
Prussian blue is an inorganic pigment (Fe4[Fe(CN)6]3) and was discovered back in the 18th century in Berlin (hence the name), whereas indigo, an organic dye extracted from plants, has been used since ancient times, until being superceeded by synthetic alternatives. Identifying which has been used can help date painting, but both are insoluble in water or many common organic solvents.
Pauk was tasked with making the pigments soluble so that they could be identified with mass spectrometry rather than traditional methods like HPLC. This was especially important, said Pauk, because when he was finally sent samples ofthe paint, they were so small that to begn with he thought he had been sent empty sample bags.
For Prussian blue, Pauk showed that the pigment could be decomposed with sodium hydroxide to give Na4[Fe(CN)6. Meanwhile, indigo could be reduced with dithionite to give the soluble leucoindigo. That allowed Pauk and his lab to test the tiny samples of paint and identify the paint used. Although the technique was so sensitive that it detected some contamination of Prussian blue, the painting was shown to mainly contain indigo, helping to date the artwork as well as telling conservators what to use.
Restoration of the artwork is still ongoing. Meanwhile Pauk is now trying to do similar work to convert Tyrian, or Royal, purple into a mass spec-able compound. If anyone has any ideas I suggest you get in contact.